Professional audio systems generally use multiple multi-way loudspeaker boxes in order to achieve and direct high levels of sound pressure in large spaces such as arenas and stadiums. Line array loudspeaker systems are typically used wherein each loudspeaker box or enclosure in the line array has multiple sound drivers for reproducing the desired wide range of sound frequencies at a high output level. Having multiple sound drivers creates problems with wave interferences at different frequencies and different locations throughout the intended listening area. Typically the intended listening area covers angular dimensions of 60 degrees vertically by 120 degrees horizontally. The interferences reduce the fidelity and clarity of the sound, particularly at larger angles from the array.
Loudspeaker systems often have one or more high frequency drivers or tweeters in the center for reproducing high frequency sound waves approximately in the range of 600 to 20,000 Hz. Sound radiating from the high frequency driver will generally radiate in all directions unless directed by waveguides or sidewalls. Thus, sidewalls and/or waveguides are generally placed adjacent each side of the high frequency driver to form an angle to direct the high frequency sound waves, with the high frequency driver located at the or near the vertex of the angle. Typically each sidewall or waveguide is angled at approximately 30-60 degrees off a center line in order to cover a 60-120 degree horizontal listening area.
Many prior art loudspeaker systems place one or more midrange frequency sound drivers adjacent the central high frequency driver(s) for emitting midrange frequency sound waves in the range of 200 Hz to 2000 Hz. The midrange drivers are often part of the sidewalls or waveguides that direct the high frequency sound waves. This can cause inconsistencies in the wave front since the midrange drivers typically have irregular surfaces that interrupt the path of the passing high frequency sound waves, introducing diffraction edges and cavities that cause reflections, creating cancellations and summations of sound waves which causes inconsistencies in the frequency response.
There have been numerous attempts to solve the aforementioned problems and to design a loudspeaker that can integrate midrange and high frequency sound sources at a high output level to produce a consistent wave front, particularly at larger angles from the loudspeaker. However each solutions has had its drawbacks. While an ideal flat frequency response may be able to be produced in certain locations in a polar response area, there is often a less than ideal frequency response in other locations in the polar response area.
U.S. Patent Publication No. 2002/0014369 to Engebretson and U.S. Pat. No. 7,333,626 to Opie et al. disclose a system for integrating mid-range and high frequency sound drivers in multi-way loudspeaker system wherein a radiation boundary integrator having foam-filled slots are placed over the mid-range drivers, on either side of the high frequency driver. The foam is substantially transparent to allow midrange sound waves to pass through the slots while preventing high frequency sound waves from passing through the slots.
U.S. Pat. No. 8,515,102 to Waller discloses a line array speaker system designed to provide a more uniform frequency response to listeners at large off-axis angles to the speakers by using different sized mid-frequency drivers. A pair of smaller mid-frequency drivers straddle a central high frequency driver and are fed a high frequency band within the midrange frequencies, and a pair of larger mid-frequency drivers straddling the smaller mid-frequency drivers and are fed with a lower frequency band in the midrange frequencies.
U.S. Pat. No. 4,031,318 to Pitre discloses an older version of a loudspeaker system wherein the mid-range speaker drivers are in a separate enclosure from the high and low frequency drivers.
U.S. Pat. No. 7,557,265 to Pazandeh teaches a speaker system having various low, mid-range and high frequency drivers. The high frequency driver is in the center and projects sound vertically upward, and the mid-range drivers project sound at an angle toward each other and toward the high frequency driver so as to intersect and cause an echo effect to improve sound spaciousness.
U.S. Patent Publication No. 2007/0263878 to Yu et al. teaches a sound mask for use on a multi-channel sound box containing more than one speaker driver. The sound mask has angled and straight circular apertures for directing the sound waves from the speaker drivers in a wider sound field. Yu et al. is not directed to professional loudspeaker systems designed to produce high sound pressure levels.
Various other prior art references, such as U.S. Patent Publication No. 2013/0336516; U.S. Pat. No. 7,035,425 and U.S. Pat. No. 8,712,091 teach speaker system designs. However these systems are not directed to professional audio systems for high sound pressure levels that include both midrange and high frequency drivers in one enclosure. U.S. Pat. No. 1,884,724 to Keller discloses a sound box for phonic diaphragms having adjustable apertures in the front of the sound box to control the operating characteristics of the sound box. U.S. Patent Publication No. 2011/0268292 to Suvanto et al. teaches an apparatus for use in devices, such as mobile devices, that have acoustic transducers.
There continues to be a need for a professional loudspeaker system that causes a coherent wave front from a loudspeaker enclosure having both high frequency and midrange frequency sound drivers for use in large venues wherein a wide frequency response area is needed.